Piezoelectric devices that employ piezoelectric bodies having piezoelectricity in which piezoelectric bodies stretch/contract according to increase/decrease in the intensity of applied electric field are used as actuators mounted on inkjet recording heads, sensors, storage devices, and the like. Recently, in the trend toward high density and high integration of devices, reduction in film thickness of piezoelectric devices has been moved forward and development of piezoelectric devices with piezoelectric films having high piezoelectric properties has been in progress.
As for piezoelectric films having high piezoelectric properties, piezoelectric films of Pb containing perovskite oxide films, such as PZT (Pb(Zr, Ti)O3: lead zirconate titanate) and the like are known. In particular, Pb containing perovskite oxide films which can be formed by vapor growth methods, including sputtering method, receive attention as films having high piezoelectric properties, but still have a problem in durability.
It is known that the durability of a piezoelectric device is restricted by the deterioration in device characteristics due to residual stress in the piezoelectric film, moisture resistance of the film, and the like. The residual stress in a piezoelectric film is likely to cause a crack or a warpage in the piezoelectric film, triggering displacement blockage of the piezoelectric device, film detachment, and the like. Further, under a high humidity environment (in particular, a high temperature and high humidity environment), leakage current of the piezoelectric film is likely to increase due to the presence of water, leading to dielectric breakdown. Still further, the high humidity environment causes ionization of a constituent element of the piezoelectric film which is likely to facilitate ion migration, whereby characteristics of the device are likely to be deteriorated.
For the purpose of improving moisture resistance, methods for preventing ion migration have been studied. Japanese Unexamined Patent Publication No. 2004-087547 discloses a piezoelectric actuator in which Pb composition of the PZT thin film is reduced adjacent to the upper electrode in order to prevent ion migration of the PZT thin film. Further, Japanese Unexamined Patent Publication No. 6(1994)-068529 discloses a ferroelectric device in which a conductive oxide electrode is used as the lower electrode and a Pb containing ferroelectric film is formed on the electrode and heated to form a conductive intermediate layer that includes composition elements of the lower electrode material and ferroelectric material, whereby the composition gradient between the lower electrode and ferroelectric film is reduced.
Both the piezoelectric actuator disclosed in Japanese Unexamined Patent Publication No. 2004-087547 and the ferroelectric device disclosed in Japanese Unexamined Patent Publication No. 6 (1994)-068529 employ a structure in which the composition of the piezoelectric film is changed within the film. If the film composition is changed to that which is different from a composition that may possibly have a perovskite crystal structure, the portion of the film may no longer maintain the perovskite crystal structure, not just changed in the composition. Accordingly, the piezoelectric property is degraded, although the ion migration is prevented.
The present invention has been developed in view of the circumstances described above, and it is an object of the present invention to provide a piezoelectric device which includes a Pb containing perovskite oxide film having an excellent piezoelectric property and durability, and a manufacturing method of the same.